Simultaneous drumming and vacuum



Patented Dec. 15, 1953 SIMULTANEOUS DRUMMING AND VACUUM TREATING OFSKINS Charles F. Rutherford, Philadelphia, Samuel Cameron Tease, Media,and Harry La Rue Troxell, Jr., Narberth, Pa., assignors to High VacuumProcesses, Inc., Philadelphia, Pa., a corporation of Pennsylvania NoDrawing. Application December 8, 1950, Serial No. 199,912

8 Claims.

This invention relates to an apparatus and method for treating leatherand skins or producing leather from skins, and more particularlyconcerns the high vacuum treatment of skins and leather with liquidtreating agents.

In conventional operations, pelts such as hides, skins of small animals,and kips, hereinafter generically referred to as skins, are firstsubmerged and soaked in clear water and left for periods up to 48 hours.The cleaned and softened skins thus produced are subjected to adepilation or unhairing process, usually involving treatment with milkof lime, which conditions the hair and epidermis, and also the fattytissues on the under side of the skin, so they are readily removed fromthe skin by mechanical methods. The unhaired skins may be subjected tothe bating and pickling process for enhancing softness and pliability,and are actually converted to leather by tumbling in a box or drumcontaining tan liquor. After tanning, the leathers are passed into abath for fixing the tannin, and are then dyed in lukewarm dye baths withmechanical working by means of a tumbler or paddle-wheel after firstgoing through a series of mechanical operations. The leather thusproduced, after drying and staking, frequently has a total areaconsiderably less than that of the hide from which it was produced, and

the proportionate decrease of total area is termed the shrinkage of thehide.

The quantity of leather produced is frequently measured in terms of thetotal square footage or area of leather, per dozen skins produced, andan undesirably high shrinkage is often observed in customary tannerypractice. It is accordingly an important object of this invention toprovide means for minimizing the extent of such shrinkage, preservinghowever the high quality of the leather produced.

Frequently unfinished leather produced in ac- Y cordance withconventional methods is subjected to an operation wherein a mixture ofoils and tanning materials is worked into the pores of the leather byrolling or tumbling in a drum. By reason of the presence ofthese addedmaterials the thickness of the leather is increased but theaforementioned operation tends to break down the skin and to decreaseits tensile strength. It is accordingly another object of the inventionto eliminate such operations, and to produce,

leather having high tensile strength consistent with thickness andminimum shrinkage.

In conventional tannery operations the hides and skins are necessarilysubjected to 9 1? Mil on of various treating liquids for rather longperiods of time. Various attempts to speed the tanning, coloring, andliming operations by in creasing strength or temperature of treatingliquids or chemicals have usually resulted in the production of inferiorleather. Accordingly it is a still further object of this invention toprovide an apparatus and process for producing high quality leather in aminimum time, and at greatly decreased cost as compared to prevailingpractice.

Other and further objects and advantages of s Unhazring The skins, whichhave been cured and are normallyreceived at the tannery in substantiallydehydrated form, are sorted, weighed and loaded directly into a rotaryvacuum drum, without preliminary soaking. This rotary vacuum drum has aplurality of radially disposed inwardly directed-pegs arrangedcircumferentially on its inner race for rotation with the drum, whichserve to lift the skins and then to drop them as the'drum'is rotated.The drum is also fitted with suitable conduits and attachmentswhereby itmay be evacuated. Care is taken during the skin-loading operation toavoid packing, or in other-words it is important to load the skinsloosely into the drum. The drum door is then closed to form an air-tightseal and the air is exhausted slowly from the drum by means of a vacuumpump. Vacuum readings for the vacuum within the drum are preferablytaken pee riodically, say every ten to fifteen minutes, for example.When a vacuum of about 15 millimeters is attained, the drum is rotatedvery slowly, at intervals of about'one-half hour, for example at a rateof 18-20 revolutions per minute, for a total of four to six revolutionsfor each half-hour period. The skins are thus lifted by the pegs,flexed, and then dropped as the drum rotates. It is found that furtherrotation at this stage may tend to crack or damage the skins to anundesirable extent, while proper evacuation is dlificult if notimpossible to achieve in a minimum time without rotation to tumble theskins when the vacuum present has reached a value in the vicinity of 15mm. Hg.

Evacuation is continued until a high vacuum equivalent to an absolutepressure of 2000500 microns Hg is attained within the drum. Such highvacuum is then held for a period of about 30-60 minutes and thevacuum'comiections to the pump are sealed off. Lining chemicals .in :theform of a homogeneous liquid or milk, at a temperature of about 85 F.,are admitted to the drum. During the course of lime introduction thevacuum drum is stationary. The lime is desirably a relatively dilutesolution or suspension and preferably consists essentially of about 30%calcium oxide, 2% caustic soda or soda ashnmd 1-2 depilatory such assodium sulfate, dimethylamine sulfate, or the composition commerciallyknown as Sebacol, for example, the foregoing percentages being by weightand based upon the total weight of dry skins present for treatment.Sebacol is a powder comprising a mixture of .sodium sulfite, sodium.bisulflte, and caustic lime.

Upon admission of the lime and complete coverage of skins by the limesolution or milk, the drum is rotated for a time under the vacuumremaining in the sealed drum, preferably for 5 minutes to one hour. Thisstep is important, the time of rotation varying with the type skinsbeing processed. The vacuum is then broken while drum rotation iscontinued by admitting air to the drum, and this is followed by furtherdrum rotation at the same speed for about onehalf to one hour. The drumis then opened and the skins are inspected for softness, pliability. anddegree of lime penetration.

By reason of the processing in accordance with the invention, the skinsare rendered soft and pliable within an unusually short period of time,on the order of approximately one-half to one hour. Treatment inaccordance with this invention eliminates the clear water soak andliming operation heretofore found necessary, in one short operation.Frequently periods of at least two days have been required, inpracticing conventional processes, merely for soaking alone.

Completeness of lime penetration is determined by cutting a skin,preferably along the backbone, which is usually most difficult topenetrate, and dropping a. standard phenolphthalein solution on the skincross section thus exposed. Dark red coloration due to phenolphthaleinaction onlime solution'indicates the extent of lime penetrationwhilellght pink coloration will appear, usually just under the grainsurface of the skin section, not reached by penetration of full strengthlime solution. By reason of treatment in accordance with this invention,excellent lime penetration is attained in the surprisingly short time ofV hour, as indicated.

The skins are now permitted to soak in the remaining lime at atmosphericpressure for a period of about 22-24 hours, with drum rotation for atleast -15 minutes during each four-hour period. Drum rotation at thispoint is important. The agitation stirs the lime suspension preventingsettling, and also flexes the skins periodically working fresh lime intothe skins.

Following the lime soak at atmospheric pressure, water is introducedinto the drum, gradually diluting the lime. The dilute lime is then runout of the drum and the skins are washed with circulating fresh water atB5-90F. They are now ready for beaming.

similar skins subjected to the conventional water soak and limingtreatment.

Coloring The coloring process of the present invention is broadlyapplicable for treating leather whether or=n0t the leather has beenbeamed or tanned, .or beamed and tanned in accordance with the highvacuum process previously set forth herein. The skins maybe beamed orlimed, unhaired, fleshed, tanned, delimed, bated, pickled and pearled inthe usual manner preparatory to coloring in accordance with the processof this invention. The pieces of leather to be colored are loadedindividually into the drum, which is then closed. Vacuum is applied inthe manner indicated in the foregoing description relating to liming,and a vacuum of 2000-500 microns Hg isithus applied to the contents ofthe drum. Coloring solution consisting essentially of 0.5-5% by weight.sulfonated oil per hundred pounds crusted weight of skins, and about15-30% by weight of basic or direct or acid dye being introduced, basedon the total crusted weight of leather stock under treatment. Forcoloring with black dyes the sulfonated oil is preferably sulfonatedmarine oil such as cod oil, sperm oil or the like. Ordinarily sulionatedoil and basic color dyes form undesirable precipitates interfering withproper leather coloring but we have found that these ingredients of thebasic coloring composition are compatible in the coloring process ofthis invention. Ordinarily the basic dye would penetrate the leatherindependently of the sulfonated oil which would merely remain in theform of a separate film on the surface of the leather; even if the oilshould be first applied to the leather, thereby effecting penetration,the subsequent application of basic color dyes would throw .thesulfonated oil back out of the leather with similar, highly undesirable,results.

Preferably the sulfonated oil and basic dye are introduced as a mixtureinto the vacuum drum. although other procedures may also he followed.These may, if found desirable in connection with the particular coloringprocess at hand, be followed by introduction of chrome, aniline, acidand direct dyes, and formic acid into the drum while maintaining theresulting vacuum. Formlc acid isintroduced into the-drum after theintroduction .of thedyes. Drum rotation is continued duringall coloradmission steps.

Following the introduction of the dyes, the drum rotation is continuedfor about 5 to 10 minutes, under .the remaining vacuum. Air is admittedinto therotating drum while the drum is rotated, rotation is continued.at atmospheric pressure for a short period, and the drum is opened forinspection of skins.

The leather is inspected for dye penetration by cutting and examining across section of the leather. Ordinarily complete penetration .of theentire cross section .of the leather piece is not required, but it isimportant that the extent of penetration be uniform throughout thepiece. Accordingly the presence of a white streak disposed substantiallyjust beneath the grain surface. bordered at both sides 'by uniformdeeply colored strips, is indicative of highly effective and uniform dyepenetration. This sort of dye penetration is attained, in unusuallyshort time, by means of the process according to our invention. Moreoverthe dyed leather has good layout, has proper feel and lies fiat withoutsurface wrinkles. Due to the uniformity and completeness of dyeabsorption little or no excess dye is found on the leather surface.

Tanning Leather may be produced from skins in accordance with theinvention by tanning in a manner substantially the same as thepreviously described coloring process, substituting tan liquor for thespecified coloring chemicals. The skins may be tanned whether or notthey have been beamed or limed in accordance with this invention, andthe advantages of minimum shrinkage, and minimum time required forretaining the skins in the tan liquor, are achieved in either case.

In all the foregoing specific examples of the invention the skins werecharged into a rotary vacuum vessel provided with means for raisingindividual skins out of the liquid and subsequently permitting them todrop into the liquor, meanwhile flexing the skins. While such means arepreferably in the form of short pegs disposed at spaced intervals on theinner circumference of a rotating drum, it will be appreciated thatequivalent means including paddle-wheels, tumblers, or the like, may beprovided for carrying out the steps of the method. It is highlyimportant to remove the skins from the liquid, flex the skins in vacuum,and re-deposit them into the liquid since otherwise the importantadvantages heretofore pointed out are not realized to the fullestextent. The skins are preferably redeposited by dropping them andpermitting free fall through a vertical drop of 4-6 feet or more,causing the skins to strike the surface of the liquid with considerableimpact.

It will be appreciated that, while a high vacuum in the range of2000-500 microns is preferred, it is within the scope of this inventionto utilize a high vacuum of about this quantity, provided adequateprocessing is attained without sacrificing the advantages of improvedshrinkage results.

It will further be appreciated that certain features of the inventionmay be used independently of the use of other features, that equivalentsteps and elements may be substituted for the steps and elementsspecifically referred to, and that reversals and other changes in thesequence of steps of the method may be made, all within the spirit andscope of the invention as defined in the appended claims.

Having thus described our invention, we claim:

1. In a method of processing skins with minimum shrinkage with asolution selected from the group consisting of unhairing, tanning andcoloring solutions, the steps which comprise charging the skins into anair-tight container, withdrawing air from said container while slowlyrotating said container, continuing the air withdrawal until a highvacuum of about 2000-500 microns mercury is attained, introducing saidsolution into said container to a level substan tially covering saidskins, and slowly rotating the container lifting the skins above theliquid level, flexing said skins in the evacuated space above the liquidlevel, and returning said skins below the surface of the liquid whilemaintaining vacuum in said container.

2. The method defined in claim 1 wherein the solution is an unhairingsolution.

3. The method defined in claim 1 wherein the solution is a tanningsolution.

4. The method defined in claim 1 wherein the solution is a coloringsolution.

5. The method defined in claim 4 wherein the coloring solution consistsessentially of about 0.55% by Weight sulphonated oil and 15-30% byweight basic dye.

6. The method defined in claim 5 wherein the sulfonated oil is asulfonated marine oil selected from the group consisting of cod oil andsperm oil.

7. The method defined in claim 1 wherein said returning step comprisesdropping said skins through a substantial distance causing them to fallsolely under the influence of gravity whereby they strike the surface ofthe solution with considerable impact.

8. The method defined in claim 7 wherein said skins are caused to fall adistance of at least about four feet.

CHARLES F. RUTHERFCRD. SAMUEL CAMERON TEASE. HARRY LA RUE TRO'XELL, JR.

References Cited in the file of this patent UNITED STATES PATENTSfacturing, pages 337 and 709, published 1941 by Rheinhold PublishingCompany, New York city.

1. IN A METHOD OF PROCESSING SKINS WITH MINIMUN SHRINKAGE WITH ASOLUTION SELECTED FROM THE GROUP CONSISTING OF UNHAIRING, TANNING ANDCOLORING SOLUTIONS, THE STEPS, WHICH COMPRISE CHARGING THE SKINS INTO ANAIR-TIGHT CONTAINER, WITHDRAWING AIR FROM SAID CONTAINER WITH SLOWLYROTATING SAID CONTAINER, CONTINUING THE AIR WITHDRAWAL UNTIL A HIGHVACUUM OF ABOUT 2000-500 MICRONS MERCURY IS ATTAINED, INTRODUCING SAIDSOLUTION INTO SAID CONTAINER TO A LEVEL SUBTANTIALLY COVERING SAIDSKINS, AND SLOWLY ROTATING THE CONTAINER LIFTING THE SKINS ABOVE THELIQUID LEVEL, FLEXING THE SKINS IN THE EVACUATED SPACE ABOVE THE LIQUIDLEVEL, AND RETURNING SAID SKINS BELOW THE SURFACE OF THE LIQUID WHILEMAINTAINING VACUUM IN SAID CONTAINER.